Manufacturers have developed various techniques for fabricating microstructures that have small feature sizes on substrates. Typically the microstructures form one of more layers of an electronic circuit. Examples of these structures include light-emitting diode (LED) display devices, polymer light-emitting diode (PLED) display devices, liquid crystal display (LCD) devices, printed circuit boards and the like. Most of these manufacturing techniques are relatively expensive to implement and require high production quantities to amortize the cost of the fabrication equipment.
One technique for forming microstructures oh a substrate includes screen printing. During screen printing, a fine mesh screen is positioned on the substrate. Fluid material is deposited through the screen and onto the substrate in a pattern defined by the screen. Screen printing requires contact between the screen and the substrate. Contact also occurs between the screen and the fluid material, which contaminates both the substrate and the fluid material.
While screen printing is suitable for forming some microstructures, many manufacturing processes must be contamination-free to produce operational devices. Therefore, screen printing is not a viable option for the manufacture of certain microstructures. For example, polymer light-emitting diode (PLED) display devices require a contamination-free manufacturing process.
Certain polymeric substances can be used in diodes to generate visible light of different wavelengths. Using these polymers, display devices having pixels with sub-components of red, green, and blue can be created. PLED fluid materials enable full-spectrum color displays and require very little power to emit a substantial amount of light. It is expected that PLED displays will be used in the future for various applications, including televisions, computer monitors, PDAs, other handheld computing devices, cellular phones, and the like. It is also expected that PLED technology will be used for manufacturing light-emitting panels that provide ambient lighting for office, storage, and living spaces. One obstacle to the widespread use of PLED display devices is the difficulty encountered to manufacture PLED display devices.
Photolithography is another manufacturing technique that is used to manufacture microstructures on substrates. Photolithography is also not compatible with PLED display devices. Manufacturing processes using photolithography generally involve the deposition of a photoresist material onto a substrate. The photoresist material is cured by exposure to light. A patterned mask is used to selectively apply light to the photo resist material. Photoresist that is exposed to the light is cured and unexposed portions are not cured. The uncured portions are removed from the substrate.
An underlying surface of the substrate is exposed through the removed photoresist layer. The cured portions of the photoresist layer remain on the substrate. Another material is then deposited onto the substrate through the opened pattern on the photoresist layer, followed by the removal of the cured portion of the photoresist layer.
Photolithography has been used successfully to manufacture many microstructures such as traces on circuit boards. However, photolithography contaminates the substrate and the material formed on the substrate. Photolithography is not compatible with the manufacture of PLED displays because the photoresist contaminates the PLED polymers. In addition, photolithography involves multiple steps for applying and processing the photoresist material. The cost of the photolithography process can be prohibitive when relatively small quantities are to be fabricated.
Spin coating has also been used to form microstructures. Spin coating involves rotating a substrate while depositing fluid material at the center of the substrate. The rotational motion of the substrate causes the fluid material to spread evenly across the surface of the substrate. Spin coating is also an expensive process because a majority of the fluid material does not remain on the substrate. In addition, the size of the substrate is limited by the spin coating process to less than approximately 12″, which makes spin coating unsuitable for larger devices such as PLED televisions.